feat: add expo-build-properties plugin to set minSdkVersion 26

Using expo-build-properties plugin for proper minSdk configuration.
Required for react-native-vad which needs Android O (API 26) or higher.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

packages/voice-mobile/app.json

@@ -22,7 +22,6 @@
       "bundleIdentifier": "com.moboudra.voicemobile"
     },
     "android": {
-      "minSdkVersion": 26,
       "adaptiveIcon": {
         "backgroundColor": "#E6F4FE",
         "foregroundImage": "./assets/images/android-icon-foreground.png",
@@ -57,7 +56,15 @@
           }
         }
       ],
-      "expo-audio"
+      "expo-audio",
+      [
+        "expo-build-properties",
+        {
+          "android": {
+            "minSdkVersion": 26
+          }
+        }
+      ]
     ],
     "experiments": {
       "typedRoutes": true,